The biggest knock against the Xbox One X is its $500 price. The PS4 Pro launched at $400 last year, and there's a good chance we'll see plenty of deals around the holidays. If your friends are on Xbox Live, or you're a devotee of Microsoft's first party franchises, then the X makes more sense. If you just want to play third-party titles that come to both platforms, though, the PS4 Pro is clearly the better deal.
If you're looking to upgrade from an original Xbox One, and you have a new TV, the One X might be more compelling. It's faster and offers more features than the One S, and more importantly, it'll last you much longer without needing an upgrade. There's also plenty of wisdom in simply waiting a while before you buy the One X, especially if you haven't moved to a 4K TV yet. The new console can make games look better on 1080p sets, since it'll supersample high-res textures and have more graphical effects, but it's simply not worth the upgrade since those TVs don't support HDR.
If price isn't a huge concern for you, it's worth considering investing in a gaming PC. A decent one costs between $600 and $800, plus the price of a monitor, but it'll easily be more powerful than the One X. And you have the added benefit of upgrading components down the line. Now that Microsoft and game publishers are offering most major titles on PC, you won't be missing out on much by ditching consoles.
Ultimately, the Xbox One X offers some major performance upgrades that gamers will notice -- especially if you're coming from an original Xbox One. But it's also a bit disappointing since it's coming a year after the PS4 Pro, and it doesn't offer VR yet. For Microsoft fans, though, none of that will matter. It's exactly what the company promised: the fastest game console ever made.